This invention relates to shock absorber devices for linearly decelerating a machine part by imposing a relatively constant force to the part over the stroke of the device and, more particularly, to a device wherein the constant decelerating force may be adjusted for use with machine parts having different weights and velocities.
Shock absorbers which force fluid through a restricted orifice to convert the kinetic energy of a moving part into an increase in the thermal energy of the fluid are commonly used on machines. The smoothest deceleration of the moving part is obtained by absorbers which offer a constant resistive force to the motion over the total length of the deceleration.
One class of such devices employs a piston connected to the machine part and movable within a cylinder having a closed end. A series of exponentially spaced holes are formed along the length of the cylinder wall and the cylinder is supported within a housing filled with fluid. As the piston is forced into the cylinder by motion of the machine part, the fluid is forced through the holes and the kinetic energy of the part is converted into thermal energy of the fluid. As the piston moves down the cylinder, it successfully closes off the holes so that the force imposed on the load is maintained relatively constant resulting in a linear deceleration of the moving part.
The force imposed on the part is a function of the configuration of the fluid orifice and linear decelerators of this class have been designed wherein the orifice configuration may be varied to accommodate the device for use with parts having varying weights and kinetic energy. One of the most common approaches is to provide grooves in a tubular sleeve fitting over the cylinder. The grooves in the sleeve cooperate with holes in the cylinder to define the fluid orifices. The angular or axial position of the sleeve on the cylinder may be adjusted to vary the orifice configuration and thus the resistance provided to the load. Representative examples of the so-called "groove on hole" shock absorbers are disclosed in commonly assigned U.S. Pat. Nos. 4,059,175; 4,298,101; and 4,321,987, as well as the disclosures in U.S. Pat. No. 3,425,522 to Gryglas and U.S. Pat. No. 3,693,767 to Johnson. Whereas shock absorbers of the groove on hole configuration have proven to be generally satisfactory in operation, the prior art groove designs have been rather complex resulting in high initial manufacturing costs; the prior art groove designs have tended to encourage laminar flow upstream and downstream of the metering orifice with a resultant variation in shock absorbing performance for a given setting as the temperature of the hydraulic fluid varies with usage; the prior art groove designs have tended to create areas of stress concentration in the sleeve so as to create a potential failure mode within the sleeve; and the prior art groove designs have tended to create areas of intensified errosive wear resulting from bombardment from contaminates in the hydraulic fluid.